Electronmicroscopic and autoradiographic studies of the epithelium and pericryptal fibroblast sheath of normal, adenomatous and carcinomatous adult human colon, of normal fetal colon, and of rabbit and rat colon will be continued and expanded. Organ culture techniques will be applied to the study of cell renewal and synthsis of extracellular products in the sheath. The pericryptal sheath of other parts of the gastrointestinal tract will also be studied. Investigations will continue on mesenchymal cell renewal in adult tissues and on the fine structure and histogenesis of soft tissue tumors. Correlated studies of corneal cell morphology and physiology will be continued using an improved perfusion technique, using biologically active agents such as cytochalasin-B which affect both parameters, and using cell culture of rabbit corneal endothelium.